Osteoarthritis is characterized by the progressive degeneration of articular cartilage, indicating that the normal balance of anabolic and catabolic activities of the chondrocytes has been severely disrupted. This project will use a precisely defined in vitro explant culture system to examine the relationship between different types of biomechanical stress in regulating matrix metabolism and inflammation, as measured by biomarkers of inflammation and matrix turnover. Our primary hypothesis is that mechanical stress interacts with certain cytokines to influence matrix metabolism in articular cartilage through the production of inflammatory mediators by chondrocytes. We propose that mechanical deformation provides an anabolic stimulus to the chondrocytes, but above a certain threshold of magnitude will result in a "switch" in the chondrocyte phenotype to a state of inflammation and matrix degradation. We hypothesize that such changes will be reflected by the profile of cartilage matrix "biomarkers" produced, and by the similarity of this profile to that produced in animal models of OA and clinical OA. The Specific Aims of this study are:1) to measure PGE> NO, COX, and NOS in explants of articular cartilage exposed to precisely controlled shear or compressive stresses; 2) to determine the influence of NO and PGE2 on matrix turnover as: measured by mRNA transcription and protein synthesis of collagen, aggrecan, and the production of cartilage biomarkers (5D4, 3B3, and BC3 epitopes of aggrecan, hyaluronan, 9A4 collagen propeptide, and cartilageoligomeric matrix protein); and 3) to determine if exogenous IL-1, IL-6, or TNF-alpha cooperate with mechanical stress to modulate chondrocyte NO and PGE2 production, matrix turnover, and biomarker production. A detailed investigation of the interactions between specific biomechanical factors, proinflammatory mediators, and tissue metabolism in articular cartilage will improve our understanding of the pathology of the OA, particularly as it relates in vivo to "biomechanical" therapies such as exercise or weight loss. The results of this study will provide new insights into key elements of the pathogenesis of OA, and will hopefully lead to the development of new pharmacologic or biophysical interventions for the prevention or treatment of disease.